Advertisement

Advertisement

Soon every summer will be too hot for corals

The future is short for the world’s corals, says the chief scientist of a global survey of reefs, but their demise must alert the world to the threat of warming

By Sean O'Neill and Catherine Brahic

“One in every four species in the ocean lives on a reef, and we’re taking away that habitat”

(Image: The University of Queensland)

How are you keeping tabs on coral?The Catlin Seaview Survey (CSS) has captured 800,000 images of coral reefs from 22 countries in four years. It’s the largest stocktake of the health of reefs worldwide in history. Right now we have an expedition in the Maldives. We really want to get good baseline data as we start to see the next coral bleaching event.

Why should we focus on coral reefs?These reefs create a microcosm story&colon; they are a metaphor for where the world is going, and one of the strongest signs of an impact of climate change on ecosystems. Over the last 30 years we’ve lost coral at an incredible rate – about 40 per cent of it globally. One in every four species in the ocean lives on a reef, and we’re taking away that habitat.

What causes coral bleaching?It happens when the sea temperature reaches roughly a degree warmer than the long-term summer maximum and stays there for four to six weeks. Corals can survive it, but if the event goes on longer, or the temperature climbs higher still, you get mass mortality. Over the last 12 months seas have come very close to that threshold. We’re on the brink of a major, worldwide bleaching event, says the US National Oceanic and Atmospheric Administration’s Coral Reef Watch programme.

Advertisement

Are these events becoming more common?Once, it might have taken the extra ocean warming of an El Niño to cause bleaching, but we’re now getting to the point where even regular temperatures are getting high enough. When we predicted this in 1999, I became a pariah. People were saying “No, that’s not possible.” But it’s coming true – no one’s been able to knock that idea off. And I think that 20 years from now, every summer will be too hot for corals&colon; they will disappear as dominant members of tropical reef systems by 2040-2050. It’s hard to argue it any other way.

How can we peer beyond that bleak outlook?Lots of people say to me, “God, you’re a depressing bastard.” But this is the scientific reality. What we’re hoping as we head towards this year’s climate summit in Paris is that we can bring this startling issue to the fore. The CSS now has a rapid-response capacity; we can quickly send people and recording equipment to bear witness to the actual moments of bleaching. The death throes of coral are, sadly, quite beautiful events.

Where is the beauty in dying coral?It happens over a week, but there comes a moment when suddenly reefs just go from being brown – from all those symbiotic algae inside their tissues – to these beautiful white translucent colours, when the algae are expelled. Pink and purple animal pigments in the coral produce beautiful fluorescing patterns. On the southern Great Barrier Reef we had some localised bleaching, and dive companies were encouraging people to come to see the fluorescing corals. I understand why they did it, but it was bizarre – like partying at a funeral.